Internal structure of a primary exhaust duct

ABSTRACT

An internal structure of a primary exhaust duct of a turbomachine. The internal structure comprises a primary wall comprising a surface of revolution, allowing air to pass through the orifices and forming an internal surface of the primary exhaust duct, an interior skin, comprising a surface of revolution, arranged inside the primary wall and extending between an upstream flank for facing toward the front of the turbomachine and a downstream flank for facing toward the rear of the turbomachine, and a plurality of spacers angularly distributed around a periphery of the interior skin and fixed between the primary wall and the interior skin. The particular way in which the interior wall is fixed makes the internal structure easier to construct and allows attenuation of noise at chosen frequencies.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of the French patent application No.1761255 filed on Nov. 28, 2017, the entire disclosures of which areincorporated herein by way of reference.

BACKGROUND OF THE INVENTION

The present invention relates to an internal structure of a primaryexhaust duct of a turbomachine, to a turbomachine comprising such aninternal structure, and to an aircraft comprising at least one suchturbomachine.

A turbomachine conventionally comprises, from upstream to downstream, anair inlet via which the air enters the turbomachine, a motor which burnsthe air with fuel, and an exhaust duct via which the burnt gases aredischarged.

Such a turbomachine generates noise when it is in operation.

In order to attenuate some of the noise, the turbomachine is surroundedby a nacelle comprising noise attenuating means such as, for example,honeycomb structures.

The low-frequency (between 300 Hz and 1000 Hz) sounds, particularlythose associated with combustion, emitted by the turbomachine duringtake-off or landing form a significant source of noise in theenvironment and, in order to attenuate this noise, it is known practiceto fit low-frequency sound attenuating devices in the structure of theprimary exhaust duct (the English term “plug” is used for this).

The primary exhaust duct is situated in the continuation of the engineand in front of the jet pipe cone and its exterior primary wall is incontact with the stream of burnt gas coming from the engine.

Document U.S. Pat. No. 7,784,283 discloses the production ofcompartments separated by dividing partitions under the perforatedprimary wall of the primary exhaust duct in order to form Helmholtzresonators.

Such a device is effective although it is necessary to find new modes ofembodiment.

SUMMARY OF THE INVENTION

It is one object of the present invention to propose an internalstructure of a primary exhaust duct of a turbomachine which comprisesdevices for attenuating low frequency noises which is simple and easy toimplement.

To that end, the invention proposes an internal structure of a primaryexhaust duct of a turbomachine, the internal structure comprising:

-   -   a primary wall comprising a surface of revolution, allowing air        to pass through the orifices and forming an internal surface of        the primary exhaust duct,    -   an interior skin, comprising a surface of revolution, arranged        inside the primary wall and extending between an upstream flank        intended to face toward the front of the turbomachine and a        downstream flank intended to face toward the rear of the        turbomachine, and    -   a plurality of spacers angularly distributed around the        periphery of the interior skin and fixed between the primary        wall and the interior skin.

The particular way in which the interior wall is fixed makes theinternal structure easier to construct and allows attenuation at chosenfrequencies.

Advantageously, each of the flanks of the interior skin lies somedistance away from the primary wall so as to leave a free passagebetween the interior skin and the primary wall.

Advantageously, the spacers are fixed to the interior skin by removablefixing means.

Advantageously, each spacer adopts the shape of a C-section with acentral wall and two flanges.

Advantageously, the central wall has a through-recess.

Advantageously, the spacer comprises a flap able to move according totemperature between a closed position in which it closes off thethrough-recess and an open position in which it does not close off thethrough-recess.

Advantageously, the flap is made from shape memory alloy.

Advantageously, the interior skin is pierced with drainage holes.

According to one preferred embodiment, the interior skin is formed bymachining a single element.

According to another particular embodiment, the interior skin is made upof several portions fixed together.

The invention also proposes a turbomachine comprising a primary exhaustduct delimited on the outside by a primary jet pipe and on the inside byan internal structure according to one of the preceding variants.

The invention also proposes an aircraft comprising at least oneturbomachine according to the preceding variant.

BRIEF DESCRIPTION OF THE DRAWINGS

The abovementioned features of the invention, together with others, willbecome more clearly apparent from reading the following description ofone exemplary embodiment, the description being given in connection withthe attached drawings among which:

FIG. 1 is a side view of an aircraft according to the invention,

FIG. 2 is a perspective view of a primary exhaust duct,

FIG. 3 is a perspective view of an internal structure of a primaryexhaust duct according to the invention,

FIG. 4 is an enlargement of a detail of the internal structure of FIG.3,

FIG. 5 is a perspective view of one example of a spacer employed in theinternal structure according to the invention, and

FIG. 6 is a view in section on the plane VI of FIG. 5, of a spaceraccording to a variant of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an aircraft 10 which comprises a wing 12 under which isfixed a nacelle 14 in which a turbomachine is housed.

In the description which follows, and by convention, the longitudinalaxis of the turbomachine, oriented positive in the direction of forwardtravel of the aircraft 10 and which is also the longitudinal axis of thenacelle 14 is referred to as X, the transverse axis which is horizontalwhen the aircraft 10 is on the ground is referred to as Y, and thevertical axis or vertical height when the aircraft 10 is on the groundis referred to as Z, these three directions X, Y and Z being orthogonalto one another and forming an orthonormal frame of reference.

In the description which follows, terms relating to a position areconsidered with reference to the direction of travel of the gasesthrough the turbomachine, namely from the front towards the rear of theaircraft 10.

FIG. 2 shows the rear part of the turbomachine which forms a primaryexhaust duct 202 via which the gases burnt by the turbomachine aredischarged and which is delimited on the outside by a primary jet pipe204 and on the inside by an internal structure 206 of the primaryexhaust duct 202.

The primary exhaust duct 202, like its internal structure 206, have anoverall shape comprising surfaces of revolution about the longitudinalaxis X of the turbomachine.

A jet pipe cone 208 is fixed at the rear of the internal structure 206.

FIG. 3 shows a view from the front and in perspective of the internalstructure 206 and of the cone 208, and FIG. 4 shows an enlargement ofthe internal structure 206.

The internal structure 206 comprises a primary wall 302 pierced withholes 304 distributed over the surface of the primary wall 302. Theprimary wall 302 forms the exterior surface of the internal structure206, namely the surface that forms the internal surface of the primaryexhaust duct 202.

The internal structure 206 comprises an interior skin 305. The primarywall 302 and the interior skin 305 each constitute a surface ofrevolution which in this example is cylindrical overall, and theinterior skin 305 is arranged inside the primary wall 302 in such a wayas to form an assembly of two coaxial surfaces.

The interior skin 305 is fixed to the primary wall 302 by spacers 307fixed between the primary wall 302 and the interior skin 305 andangularly distributed around the periphery of the interior skin 305. Thespacers 307 can be seen as hidden detail in FIGS. 3 and 4.

The interior skin 305 extends between an upstream flank 402 orientedtowards the front of the turbomachine and a downstream flank 404oriented towards the rear of the turbomachine. Each flank 402, 404 hereadopts the shape of a crown.

As shown in FIG. 4, the interior skin 305 and the primary wall 302 arenot fixed to one another. What this means to say is that each of theflanks 402 and 404 of the interior skin 305 lies some distance away fromthe primary wall 302, so as to leave a free passage 309 which allows airto circulate freely between the interior skin 305 and the primary wall302.

The interior skin 305 is thus fixed only by the spacers 307, making theimplementation easier because there is no need to provide a connectionbetween the primary wall 302 and the interior skin 305. Furthermore, thepassage 309 makes it possible to afford better absorption of the soundscaused by vibrations of the interior wall 305 brought about by the factthat its flanks 402 and 404 are not fixed.

Between two consecutive spacers 307, the volume between the interiorwall 305 and the primary wall 302 forms a box constituting a Helmholtzresonator.

In order to allow ease of demounting of the interior skin 305, thespacers 307 are fixed to the interior skin 305 using removable fixingmeans such as screws, for example and, for that purpose, the interiorskin 305 and the spacer 307 have bores 405 provided for that purpose.The removable fixing means are elements which can be taken out withoutdamaging the interior skin 305 and the spacers 307.

The fixing of each spacer 307 to the primary wall 302 may be performedby using removable fixing means such as screws or permanent fixing meanssuch as welding, for example.

In the invention embodiment depicted in FIGS. 3 to 6, each spacer 307takes the form of a C-section with a central wall (504 in FIG. 5) andtwo flanges (506 a-b in FIG. 5), although other forms are possible suchas, for example, the shape of posts or of profile sections of differentshapes.

In the case of a spacer 307 having a C-section profile, the spacer 307is fixed to the interior skin 305 and to the primary wall 302 using oneof the flanges 506 a-b of the C-section profile and, where appropriate,the interior skin 305 or the primary wall 302.

According to one first exemplary embodiment of the invention depicted in

FIG. 3, the spacer 307 takes the form of a C-section profile, thecentral wall 504 of which is solid.

FIG. 5 shows a spacer 507 with a C-section profile according to a secondparticular form of embodiment and FIG. 6 shows a spacer 607 with aC-section profile according to a third particular embodiment.

In the embodiment of FIG. 5, the spacer 507 has a central wall 504 whichexhibits a through-recess 502 so as to provide better communicationbetween the boxes.

In the embodiment of FIG. 6, the spacer 607 has a central wall 504 witha through-recess 502 and a flap 602 which is able to move on the spacer607 and according to temperature, between a closed position (in solidline) in which it closes off the through-recess 502, and an openposition (in chain line), in which it does not close off thethrough-recess 502. Thus, as the frequencies of sound vary as a functionof temperature, the opening of the flap 602 can be adapted to theambient temperature and thus allow optimal absorption of sound whateverits temperature. In general, the flap 602 is designed to open upon anincrease in temperature and to close upon a drop in temperature.

In order for the positioning of the flap 602 to be consistent with thetemperature, the flap 602 is made of a shape memory alloy having a shapeand characteristics which are suited to the temperature range that is tobe covered.

In order to remove any water which may infiltrate, the interior skin 305is pierced with drainage holes 406.

The interior skin 305 is preferably formed by machining a singleelement, but could equally be made up of several portions joinedtogether, particularly by welding.

While at least one exemplary embodiment of the present invention(s) isdisclosed herein, it should be understood that modifications,substitutions and alternatives may be apparent to one of ordinary skillin the art and can be made without departing from the scope of thisdisclosure. This disclosure is intended to cover any adaptations orvariations of the exemplary embodiment(s). In addition, in thisdisclosure, the terms “comprise” or “comprising” do not exclude otherelements or steps, the terms “a” or “one” do not exclude a pluralnumber, and the term “or” means either or both. Furthermore,characteristics or steps which have been described may also be used incombination with other characteristics or steps and in any order unlessthe disclosure or context suggests otherwise. This disclosure herebyincorporates by reference the complete disclosure of any patent orapplication from which it claims benefit or priority.

1. An internal structure of a primary exhaust duct of a turbomachine,the internal structure comprising: a primary wall comprising a surfaceof revolution, allowing air to pass through orifices at each end of thesurface of revolution and forming an internal surface of the primaryexhaust duct, an interior skin, comprising a surface of revolution,arranged inside the primary wall and extending between an upstream flankconfigured to face toward the front of the turbomachine and a downstreamflank configured to face toward the rear of the turbomachine, and aplurality of spacers angularly distributed around a periphery of theinterior skin and fixed between the primary wall and the interior skin.2. The internal structure according to claim 1, wherein each of theupstream flank and downstream flank of the interior skin lies somedistance away from the primary wall so as to leave a free passagebetween the interior skin and the primary wall.
 3. The internalstructure according to claim 1, wherein the spacers are fixed to theinterior skin by removable fixing means.
 4. The internal structureaccording to claim 1, wherein each spacer adopts a C-section shape witha central wall and two flanges.
 5. The internal structure according toclaim 4, wherein the central wall has a through-recess.
 6. The internalstructure according to claim 5, wherein the spacer comprises a flapconfigured to move, according to temperature, between a closed positionin which the flap closes off the through-recess and an open position inwhich the flap does not close off the through-recess.
 7. The internalstructure according to claim 6, wherein the flap is made from shapememory alloy.
 8. The internal structure according to claim 1, whereinthe interior skin is pierced with drainage holes.
 9. The internalstructure according to claim 1, wherein the interior skin is formed bymachining a single element.
 10. The internal structure according toclaim 1, wherein the interior skin is made up of several portions fixedtogether.
 11. A turbomachine comprising a primary exhaust duct delimitedon an outside by a primary jet pipe and on an inside by an internalstructure according to claim
 1. 12. An aircraft comprising at least oneturbomachine according to claim 11.